The decision appears to underscore deepening US concern about the course taken by the Arab world's most populous country, reeling from violent street clashes following Mursi's July 3 overthrow.

Still, Obama administration officials offered no hint that the decision on the F-16s signaled a shift in broader US policy on aid to Egypt. Washington still has not decided whether to call Mursi's overthrow a coup, something that would legally trigger a cut-off in US assistance.

However, suggesting mounting impatience with Egyptian generals' handling of the situation after Mursi's ouster, an administration official said one of the main objectives was to press the military-led government in Cairo to "move forward and get this democratic transition correct."

US Defense Secretary Chuck Hagel informed Egypt's military chief, General Abdel Fattah al-Sisi, of Obama's decision to halt the delivery of the F-16s in a phone call on Wednesday, the Pentagon said.

"Given the current situation in Egypt, we do not believe it is appropriate to move forward at this time with the delivery of F-16s," Pentagon spokesman George Little said, referring to the situation on the ground as "fluid."

Sisi has called for mass rallies on Friday to give him a mandate to tackle surging violence, fanning fears within Mursi's Muslim brotherhood of a military crackdown. The Muslim Brotherhood has warned of possible civil war.

Sporadic street clashes in recent days have killed more than 100. An overnight bomb attack on a police station north of Cairo killed one person and wounded two dozen.